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1140                           Appendix VL

delivered under pressure to the bearing pipes cc, and then by the
channels D D E in the crank shaft to the crank pins. From the
crank-pin journals it travels through pipes FFF to the gudgeons,
and finally to the crosshead slides, whence it returns to the tank.
Two important things have been secured : (i) the oil has been
fed under a pressure of 10 Ibs. per sq. in. to all the moving pins
and journals, so that the shock of reversal is taken by a fluid
which is elastic through leakage but yet highly resistant, and
(2) the engine has been efficiently lubricated. Practically any
1 knock/ however severe, can be taken up by this method, though
f ,                      of course lack of balance is always finally transferred to the

i                      foundations and felt as vibration.    The  steam first enters the

i                      chamber K, and is distributed to the high-pressure cylinder H,

from which it is exhausted to the low-pressure cylinder j.    The
governor K is of the same type as that on p. 893.

1                           P. 640.    Link Motion.

;!                           Equivalent Crank.—Let OD, Fig. 1007, be an engine-crank,

A                      and o A, o B two eccentric cranks, whose radii are r and r1 and

4                      whose advance angles are a and a: respectively.    It is required

||                      to find a single crank that will give the same motion to c that the

'|!                      combined cranks will give. Complete the parallelogram o A B E, and

I                      the diagonal R will be the equivalent crank.     For, dropping per-

Ipendiculars to Ax ^ EX ;   OAI = EIEI and therefore the motion
due to R will equal o BX + o Aa or that due to the cranks r and r±
taken together.    If A and B be now coupled to link a br whose
j                      mid point is c; the slide d will only receive half the travel due to

1                      equivalent crank R.

|                           In Fig. 1008 we require a crank that will give the relative

I                      motions of the slides d e as caused by the cranks r and rlt   Join

I                      A B and complete the parallelogram E B, when R will be the

|                      required   crank.     For  o Er = AJ BJ,  which   is   the   differential

motion OAi-OBi excepting for change of sign, which puts OE

in the left quadrant.

In Fig. 1009 two cranks are connected to a link where the

C B

valve spindle c is not centrally adjusted,   c will receive —

A B

of A'S motion plus — of B'S motion.    To find the equivalent

A B